1. Field of the Invention
The present invention relates to a silicon carbide semiconductor device manufacturing method.
2. Background of the Related Art
Compound semiconductors, such as silicon carbide four layer repeat hexagonal crystals (4H—SiC), are commonly known as semiconductor materials. When fabricating a power semiconductor device using 4H—SiC as a semiconductor material, a 4H—SiC single crystal film (hereafter referred to as “a SiC epitaxial film”) is epitaxially grown on a semiconductor substrate formed of 4H—SiC (hereafter referred to as “a 4H—SiC substrate”), thereby fabricating a SiC single crystal substrate. To date, a chemical vapor deposition (CVD) method is commonly known as an epitaxial growth method.
Specifically, a SiC single crystal substrate, wherein a SiC epitaxial film is deposited using a chemical vapor deposition (CVD) method, is fabricated by a raw material gas fed into a reactor (chamber) being thermally decomposed in a carrier gas, and silicon (Si) atoms being continuously deposited in line with the crystal lattice of a 4H—SiC substrate. Commonly, monosilane (SiH4) gas and dimethylmethane (C3H8) gas are used as raw material gases, while hydrogen (H2) is used as a carrier gas. Also, nitrogen (N2) gas or trimethylaluminum (TMA) gas is added as appropriate as a dopant gas.
Existing epitaxial growth methods are such that growth speed is generally in the region of several μm/hour, because of which it is not possible to grow an epitaxial film at high speed. Consequently, a large amount of time is taken to grow an epitaxial film of the thickness of 100 μm or more necessary in order to fabricate a high breakdown voltage device, because of which an increase in epitaxial growth speed is required for industrial production. Also, a high breakdown voltage device is such that, as an epitaxial film of a thickness of 100 μm or more is provided as a drift layer, the further breakdown voltage is increased, the greater conduction loss becomes.
In order to reduce conduction loss, it is necessary to cause conductivity modulation due to minority carrier implantation by increasing the carrier lifetime of the drift layer, thereby reducing on-state voltage. Consequently, in order to increase the carrier lifetime of the drift layer, it is necessary to reduce crystal defects forming lifetime killers that exist in the epitaxial film. For example, point defects known as Z1/2 centers and EH6/7 centers that exist in an energy position lower than the bottom (Ec=0) of a conduction band (at a deep level) are commonly known as crystal defects that exist in an n-type SiC epitaxial film and form lifetime killers.
It has been reported that the Z1/2 centers and EH6/7 centers are crystal defects caused by carbon (C) vacancies in a SiC epitaxial film. For example, refer to L. Storasta, et al., “Deep levels created by low energy electron irradiation in 4H—SiC”, AIP: Journal of Applied Physics (USA), American Institute of Physics, Jan. 1, 2004, Volume 96, Issue 9, Pages 4,909 to 4,915 (Non-Patent Literature 1). Consequently, in order to reduce the crystal defects in a SiC epitaxial film, it is necessary to form a SiC epitaxial film with few carbon vacancies. A method whereby, after a SiC epitaxial film is formed using a chemical vapor deposition method, carbon ion implantation and heat treatment, or long-time sacrificial oxidation, is further carried out has been proposed as a method of reducing the carbon vacancies in a SiC epitaxial film. For example, refer to L. Storasta, et al., “Reduction of traps and improvement of carrier lifetime in 4H—SiC epilayers by ion implantation”, AIP: Applied Physics Letters (USA), American Institute of Physics, 2007, Volume 90, Pages 062116-1 to 062116-3 (Non-Patent Literature 2) and T. Hiyoshi, et al., “Reduction of Deep Levels and Improvement of Carrier Lifetime in n-Type 4H—SiC by Thermal Oxidation”, APEX: Applied Physics Express, Applied Physics, 2009, Volume 2, Pages 041101-1 to 041101-3 (Non-Patent Literature 3).
However, the disclosures of Non-Patent Literature 2 and 3 are such that, after fabricating a SiC single crystal substrate wherein a SiC epitaxial film is deposited on a 4H—SiC substrate, it is necessary to carry out a step for reducing carbon vacancies in the SiC epitaxial film in addition to steps of forming an element structure on the SiC single crystal substrate, and there is a problem in that throughput decreases.
The invention, in order to resolve the challenges of the heretofore described existing technology, has an object of providing a method of manufacturing a silicon carbide semiconductor device with a long carrier lifetime, without carrying out an additional step after fabricating a silicon carbide single crystal substrate using a chemical vapor deposition method.